Inaccessible or confined areas such as, for example, the interior parts of gas turbine engines, often require routine inspection to verify the integrity of internal engine parts and maintain safe operation of the engine by identifying potential problems, i.e., defects in a part, prior to failure of the part, or to identify the source of an existing problem. For example, problems may be identified through visual inspection by use of a borescope, such as during routine downtime maintenance of the gas turbine engine.
Additional optical monitoring of the turbine engine may be performed during operation of the engine to further identify the condition of components located within the hot gas path of the engine. Optical monitoring of engine components during operation of the engine requires that optical elements be placed inside the engine, potentially exposing them to temperatures that are higher than the operable range of the optical materials. In a known system, external cooling has been added to the system in the form of compressed cool air, water or liquid nitrogen to cool the optical elements below the maximum operable temperature. This solution has typically added substantial complexity and additional cost to the optical system. Further, since the optical elements must be cooled continuously during operation of the engine, it is preferable to utilize such externally cooled systems on only a short term basis.